Method for filtering mobile telephone communications and related device

ABSTRACT

A method of filtering calls between a mobile network provided with frequency channels and mobile telephones registered with this mobile network. When the mobile telephones are located in a control area (N 0 ), the mobile network includes cells (Zi) associated with respective relays (Ri) each transmitting data specific to their associated cell through a beacon channel among one of the frequency channels of the network. The method includes the parametering in neighboring cells of the control area of a frequency channel of the network corresponding to a transmission channel of a transmitter (D) associated with the control area. The transmitter is never connected to the mobile network so as to operate completely autonomously.

The present patent application is a non-provisional application ofInternational Application No. PCT/FR01/03489, filed Nov. 9, 2001.

BACKGROUND

1. Field

The present invention generally relates to mobile telephone system.

2. Description of the Related Art

More specifically, the invention relates to a method for filtering callsbetween a given mobile network and a mobile telephone of this networklocated in a determined place.

And still more specifically, the invention enables filtering the callsof a particular network at a determined place, preferably a networkoperating according to the GSM standard, or the UMTS standard.

The considerable boom in mobile telephones, while constituting anadvantage in many respects, also entails certain drawbacks.

In particular, it would be desirable to limit, or even prohibit thecommunication of such equipment in certain places; for example, the casemay be cited of theaters, churches, or other public or private premiseswherein it is undesirable that mobile user conversations should disturbthe environment.

It would thus be advantageous to enable operators running mobilenetworks (e.g. Itinéris—registered trademark—in France) to set upfiltering for their subscribers' calls when they are in certain places.

This would, in fact, constitute an improvement in the service providedby the operator.

Broadband jamming devices are known, which can be used for neutralizingall mobile telephone communications.

But a major drawback associated with these devices is that theyneutralize all the incoming and outgoing radio communications of allequipment over a very wide frequency band without distinction, anddisrupt the operation of equipment having nothing to do with the mobilenetwork whose calls it would be desirable to filter.

Moreover, regulatory constraints require certain types of calls not tobe restricted, for example mobile users' calls to certain emergencyservices; the above-mentioned broadband jammers obviously do not observethis legal obligation.

Furthermore, jamming devices are known from FR 2 764 145 and FR 2 764144 whose purpose is to limit the volume to be jammed by adapting thepower of the jamming signal according to the volume and configuration ofthe space to be protected.

In these devices, the jamming signal is transmitted while sweeping thefrequency ranges used by radio telephones. But such devices, which carryout jamming over all the frequencies used by radio telephones, disruptthe general operation of the network, in particular in cells locatedclose to the area to be protected.

In addition, in this case the jamming is “brutal”, users entering thearea to be protected not having the possibility of ending theircommunications.

A jamming device is also known from FR 2 779 610 detecting the presenceof mobiles in a given area. But here again, the jamming disrupts theoperation of the network and does not allow users to end theircommunications, which is a major drawback.

SUMMARY

The object of the invention is to meet the above-mentioned needs andconstraints (it will be seen that a preferred application of theinvention relates to the filtering of calls on a network operatingaccording to the GSM standard—it should be pointed out, however, thatthe invention also applies to networks operating in accordance withstandards similar to the GSM standard, for example the UMTS standard).

In order to achieve this object, the invention provides a method offiltering calls between a mobile network provided with frequencychannels and mobile telephones registered with this mobile network, whenthe mobile telephones are located in a control area, the mobile networkcomprising a plurality of cells associated with respective relays eachtransmitting data specific to their associated cell through a beaconchannel among one of the frequency channels of the network,characterized in that the method includes the parametering in theneighboring cells of the control area of a frequency channel of thenetwork corresponding to a transmission channel of a transmitterassociated with said control area, said transmitter not being connectedto the network.

Other aspects of the method according to the invention are as follows:

-   -   said transmitter transmits on its transmission channel through        logical channels similar to those of a beacon channel of a cell        relay, in particular through a BCCH logical channel,    -   the transmission of said transmitter is accepted by the mobile        telephones located within said control area (N0) as a beacon        channel transmission of an additional cell of the network, so        that the transmission area of said transmitter is a candidate        for the selection/reselection procedures, and the incoming calls        to mobiles having selected/reselected the transmitter of said        control area are neutralized,    -   no receiver is associated with said transmitter, so that when a        mobile telephone transmits an access request on the RACH logical        channel of said transmission channel, a reselection of        neighboring cells will be automatically initiated, for want of        any response,    -   the transmitter is associated with reception means capable of        decoding the contents of random access messages transmitted by        the mobile telephones located within the control area, so as to        prohibit outgoing calls from said mobile telephones to the        network,    -   the reception means associated with the transmitter are capable        of identifying the CHANNEL REQUEST type access request messages        transmitted by a mobile telephone seeking to be connected to the        network,    -   the transmitter is also associated with a memory including a        call types file, and with means for determining the reason for        the access request of a mobile telephone, and the transmitter        receiving a CHANNEL REQUEST type access request:        -   does not send any response to the mobile telephone, causing            a reselection of a network cell by the mobile, in the event            that the reason for the mobile telephone's access request            corresponds to a determined reason,        -   transmits on its transmission channel an IMMEDIATE            ASSIGNMENT REJECT type message indicating that no request is            acceptable at the moment, in the event that the reason for            the mobile telephone's access request does not correspond to            said determined reason,    -   so that the outgoing call from the mobile telephone will only be        routed to the network if the reason for the call corresponds to        a determined reason,    -   the transmission of said transmitter is performed according to a        time framing of eight time intervals, only the first time        interval of each frame actually being used for the transmission        of certain logical channels,    -   the transmitter transmits a list of beacon channels of cells        which are its neighbors,    -   the location area parameter transmitted on the transmitter's        transmission channel is identical to the location area parameter        of the beacon channels of the surrounding cells,    -   means are provided for changing the state of a parameter        transmitted on the transmission channel of said transmitter, in        order to bar the area associated with the transmitter so that        the mobile telephones camping on said area associated with the        transmitter automatically reselect a new cell,    -   the transmission channel of said transmitter is registered in a        list of beacon channels of neighboring cells, for each cell of        the network located close to said transmitter,    -   network cell relays broadcast on the BCCH channel, in addition        to a first list of beacon channels of candidate cells for        selection/reselection procedures, a second list of beacon        channels of candidate cells for the handover procedure, and the        transmission channel of said transmitter, stored in the list of        candidate cells for selection/reselection of the neighboring        cells, is not stored in the second list of these neighboring        cells.

And the invention also relates to a device for implementing such amethod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first relay R1 transmitting radio waves over ageographical area or cell Z1.

FIG. 2 illustrate a schematic top view of cells Z1, Z2 and Z3 associatedwith respective relays, R1, R2 and R3.;

FIG. 3A illustrates an area N situated at the center of cells Z1, Z2 andZ3.

FIG. 3B illustrates distribution of the field levels associated withcells.

DETAILED DESCRIPTION OF THE INVENTION

Referring first of all to FIG. 1, we will recall certain arrangements ofthe operation of a mobile telephone network. The embodiment of theinvention disclosed on the basis of these reminders is a mobile networkoperating according to the GSM standard, which as has been stated formsa preferred, but not restrictive, application field of the invention.

Accordingly, certain reference documents are recalled, describingimportant aspects of the GSM standard:

-   -   GSM 05.08 (I-ETS 300 034-1 v. 3.8.0): Digital cellular        telecommunication system: Radio subsystem link control (Phase        1),    -   GSM 05.08 (ETS 300 578 v. 4.18.2): Digital cellular        telecommunication system: Radio subsystem link control (Phase        2),    -   GSM 03.22 (ETS 300 535 v. 4.11.0): Digital cellular        telecommunication system: Functions related to mobile station        (MS) in idle mode (Phase 2),    -   GSM 11.10 (I-ETS 300 020-1 v. 3.18.0): Digital cellular        telecommunication system: Mobile station conformity        specifications (Phase 1),    -   GSM 11.10-1 (ETS 300 020-1 v. 4.18.0): Digital cellular        telecommunication system: Conformance specifications (Phase 2),    -   GSM 04.08 (ETS 300 557 v. 4.23.1): Digital cellular        telecommunication system: Mobile radio interface Layer 3        specification (Phase 2).

This figure schematically depicts a first relay R1 transmitting radiowaves over a geographical area or cell Z1, enabling a mobile network tocommunicate in the upward and downward direction with mobile telephones.

A second relay, R2, is also depicted, which covers a cell Z2 adjacent tothe cell Z1.

The relays R1 and R2 obey a set of protocols some of whose main aspectswill be briefly described further on in this text.

These protocols are associated with the GSM standard; however, theirgeneral principles are also applicable to networks operating accordingto other standards, for example the UMTS standard.

An operator will thus be able to have a given geographical territorycovered by a network thanks to a plurality of cells Zi analogous to thecells Z1 and Z2, each cell Zi being associated with atransmission/reception relay Ri for communicating with the mobiles, eachrelay Ri being connected to the mobile network.

To ensure continuous coverage of this territory, it is necessary toprovide an overlap area between two adjacent cells, which isschematically depicted here by the hatched area R.

A user subscribed to the network thus has the possibility ofcommunicating with the network thanks to his mobile, via theintermediary of one of the relays of this network.

And relay changing procedures are provided so that, in the event thatthe user moves around the territory, his mobile is associated with therelay for communicating with the network under the best conditions.

These procedures include:

-   -   The selection procedure, which enables the mobile to choose a        network cell when it is switched on,    -   The reselection procedure, which enables a mobile already        switched on but not in communication to reselect a new network        cell, in particular when the user equipped with his mobile moves        around the territory,    -   The intercellular automatic transfer procedure (“handover”, or        HO according to widespread English language terminology), for        transferring a mobile during communication to a new cell—and        thus enabling the user to move about while constantly        communicating with the network under the best conditions.

These procedures are continuously active for each cell and for eachmobile of the network; they are constantly repeated when the mobileterminal moves around.

And an important parameter that enables these procedures to choose oneof the network's cells for a given mobile, is the field level parameterC1 received by the mobile.

This parameter C1 is defined as follows:

-   -   C1=(A−Max(B, 0)). In this formula, all the parameters are        expressed in dBm.

The parameter A is defined as follows:

-   -   A=(level received averaged over several iterations of the        abovementioned procedures)−RXLEV_ACCESS_MIN, with:        -   RXLEV_ACCESS_MIN being a parameter defined as the minimum            value of the level received enabling the network to be            accessed.

The parameter B is defined as follows:

-   -   B=MS_TXPWR_MAX_CCH−P, with:        -   MS_TXPWR_MAX_CCH: parameter corresponding to the minimum            power level allowed for the mobile when accessing the            network,        -   P: maximum output power of the mobile.

It is also possible to use a different parameter for theselection/reselection/HO procedures, representative of the level(expressed in dB for example), and/or of the quality of communicationbetween a given mobile and cell (application to a UMTS network forexample). It is also possible to use several different parametersaccording to the procedure, and according to the requirements.

By way of example, some versions of the GSM standard, for example, use aparameter C2 used during reselection, in combination with the parameterC1.

This parameter C2 is defined as follows:

-   -   C2=C1+CELL_RESELECT_OFFSET−TEMPORARY_OFFSET        -   H(PENALTY_TIME−T) if a parameter PENALTY_TIME is equal to            11111 (in binary language),        -   C2=C1−CELL_RESELECT_OFFSET if the parameter PENALTY_TIME is            other than 11111, all the parameters here again being            expressed in dBm, with:        -   PENALTY_TIME, CELL_RESELECT_OFFSET and TEMPORARY_OFFSET:            parameters linked to each cell, broadcast via the cell relay            on the cell's BCCH channel,        -   T: counter linked to the cell, being incremented from 0 up            to the value PENALTY_TIME as soon as the cell is entered in            a BA(BCCH) list of another cell—a definition will be given            below of the BCCH channel (according to the widespread            English language acronym Broadcast Common Control Channel)            and of the BA(BCCH) list of a cell.

The BCCH channel of a cell is broadcast on a radio channel chosen fromthe channels usable by the network for enabling mobiles to communicatewith the cell relays (the primary GSM band thus comprising 124 radiochannels, each with a width of 200 KHz).

The radio channel that broadcasts a BCCH channel may also be referred toby the term “beacon channel”. And more generally, either of the terms“beacon channel” and “BCCH” may equally be used to refer to thetransmission channel of a cell, and the transmission on this channel.

Each cell may thus have a particular BCCH channel, and each cellbroadcasts a BA(BCCH) list of neighboring cells in the form of a list ofnumbers of radio channels on which the BCCHs of these neighboring cellsare broadcast.

For these purposes, the operator of the mobile network sets theparameters of the BA(BCCH) list of the BCCHs (beacon channels) of theneighboring cells in the relay of each cell of the network. And theoperator can update this parameter setting as he/she wishes.

And this BCCH is thus used by each cell to broadcast parameters such asthe PENALTY_TIME, CELL_RESELECT_OFFSET and TEMPORARY_OFFSET parametersdescribed above, as well as other parameters of state of the cell,destined for mobiles capable of communicating with the cell since theyare located in the area associated with the BCCH.

These other parameters of state include among others:

-   -   CELL_BAR_ACCESS, binary parameter that can take two values: 0 if        the cell is available for routing mobile communications, 1 if it        is unavailable (the cell is then said to be “barred”),    -   CELL_BAR_QUALIFY, which is used during reselection in        combination with the parameter C2 mentioned above.

Moreover, each cell keeps a list of BCCHs of the neighboring cells up todate in a memory associated with it, and broadcasts this list on its ownBCCH.

And each cell also has, among the network channels, logical channelsother than its BCCH, for routing mobile communications.

Communications take place on all these channels according to a recurrenttime framing of eight time intervals (TI). The initial TI will thus bereserved for the BCCH, the next 7 TI being free for the communication ofmobiles with the network.

And the transmissions/receptions within each TI are themselves organizedin logical frames by time and/or frequency division, thus defininglogical channels; thus there will be several logical channels within thesame TI (which is repeated every eight TI), each able to be dedicated tothe transmission or reception of information and particular parameters.

Thus, within the BCCH channel of a given cell, each of the differentbroadcast parameters is associated with a predefined logical channel.

And each mobile can further store in its memory one or more lists ofBCCH channels—which amounts to one or more lists of cells, given thatthe BCCHs of the different cells are registered and stored in a centralmemory of the network.

In particular, each mobile can store a BA(BCCH) list of candidate cellsfor the selection and reselection procedures.

When it is in communication with the network, each mobile further uses aBA(SACCH) list of neighboring cells of BCCH candidates solely for theHO, this list being separate or not from the BA(BCCH) list.

The main steps of the selection and reselection procedures, which form astarting point of the invention will now be briefly explained.

The selection procedure, as has been stated, enables choosing a networkcell when it is switched on.

In the event that no BCCH list is stored in the mobile seeking a cell,the selection procedure follows the following steps:

-   -   during a first step, the mobile sweeps all the radio channels of        the network (for example, 124 channels for a primary GSM band        network, 374 channels for a network operating according to the        DCS 1800 standard, 174 channels for the extended GSM band        standard). During this sweep, the mobile evaluates the reception        level of each channel and calculates the averaged received        level, corresponding to the parameter A mentioned above. This        averaged received level calculation is performed on at least 5        level measurements per channel, carried out at regular intervals        over a period of 3 to 5 seconds.    -   during a second step, the mobile chooses the channel having the        highest averaged received level and determines whether this        channel is a BCCH channel of a cell;        -   if the channel in question is a BCCH, the mobile tries to            synchronize on this channel and reads the contents of this            BCCH. If the information read on this BCCH indicates that            the associated cell is eligible (in particular parameter            CELL_BAR_ACCESS=0), then the mobile chooses this cell for            communicating with the network (the mobile is said to “camp”            on the cell). If this cell belongs to the mobile's network            but is not eligible, the mobile will consult the list of            BCCHs of neighboring cells broadcast by this cell for            continuing its selection procedure,        -   if the channel having the highest averaged received level is            not a BCCH, then the mobile chooses the channel whose            averaged received level is immediately below the channel            previously chosen, then repeats the procedure disclosed            above.

In the case now where the mobile has a list of BCCH in memory when it isswitched on, the mobile will first use the channels in this BCCH listfor conducting the selection procedure according to the second stepdisclosed above.

During this procedure, if a cell considered belongs to the desirednetwork but is not eligible, the mobile will use the list of BCCHsbroadcast by this cell for completing its search.

If at the conclusion of this first search phase, based on the list ofBCCHs that the mobile had stored in memory, no eligible cell has beenfound, then the mobile resumes the selection procedure as if no list ofBCCH had been stored in memory, omitting the channels already examined.

At the time of the initial selection, only the reception level of eachBCCH is taken into consideration. If the parameter C1 of the cellinitially selected by the mobile subsequently proves to be inferior tothat of another eligible cell, the selection will be followed by areselection in accordance with the steps disclosed below.

The main steps will now be disclosed for the reselection procedure,which enables the mobile in idle mode to continuously choose the mostfavorable cell for communicating with the network.

At the conclusion of the selection procedure, the mobile camps on acell, but it continues to monitor the BCCHs present in its BA/(BCCH)list.

For this, for each BCCH present in this list, the mobile keeps a slidingaverage of the received level up to date (the duration of the averagingbeing generally between 5 and 60 seconds, or even less for some advancedversions of networks).

The level of the service cell on which the mobile is camped, is alsomonitored by the mobile at regular intervals (at a frequency rate notexceeding 5 seconds).

A minimum sampling of 5 measurements is required for calculating thisaveraged level. The same number of sampling measurements is required forthe other BCCHs present in the BA/(BCCH) list (this also being valid forthe BA/(SACCH) list), these measurements having as far as possible to bedistributed uniformly over time over the period of averaging.

Each mobile thus regularly updates the list of the six BCCH carriershaving the highest level; these six BCCH belong to the BA(BCCH) listbroadcast by the cell on which the mobile is camped.

In order to make sure that it camps on the most appropriate cell, eachmobile performs the following operations:

-   -   at least every 5 seconds, the mobile calculates the value of the        parameter C1 (and if necessary C2) for the service cell, and for        the six highest level cells,    -   the mobile reselects a new cell as the service cell if one of        the following conditions is met:        -   the parameter C1 of the service cell becomes negative, for a            period of more than 5 seconds (condition RS1),        -   the mobile detects a fault linked to the recognition of            paging messages (condition RS2),        -   the service cell enters a “barred” state, i.e. its            CELL_BAR_ACCESS parameter has a value equal to 1 (condition            RS3),        -   in the event that the reselection procedure uses the            parameter C2 as mentioned above, the parameter C2 of one of            the cells monitored by the mobile becomes greater than the            parameter C2 of the service cell for a period of more than 5            seconds. If this new cell belongs to a new location area,            the parameter C1 of this new cell must, for a period of more            than 5 seconds, exceed the parameter C1 of the initial            service cell by an amount at least equal to a predetermined            value, recorded in a parameter CELL_RESELECT_HYSTERESIS. The            latter parameter, broadcast by the BCCH of each cell, may            have a value between 0 and 14 dB in increments of 2 dB            (condition RS4),        -   the mobile's attempts at accessing the service cell remain            unsuccessful after a number of tries greater than a            predetermined value MAX_RETRANS; so if for any reason the            service cell “does not answer” the mobile, the latter            resumes the reselection procedure for searching for a new            service cell (condition RS5).

It will be noted that in the event that the above-mentioned conditionRS4 is involved (which implies that the network is using the parameterC2), reselecting a new service cell value may only occur after a delayof 15 seconds.

In the event of a reselection based on one of the other conditionsmentioned above, reselection is immediate; however, the mobile's returnonto the initial service cell is only possible after a period of 5seconds has elapsed.

When the mobile has identified a new service cell by the reselectionprocedure, it reads the BCCH channel of this new cell in order to makesure that the parameters of this cell assigning the reselection have notchanged.

If such is not the case and one of these parameters has been modifiedsince it was first read by the mobile during the reselection procedure,the mobile must check that the reselection condition is still met.

And in the event that reselection is expressed in a change of locationarea (the location area being an intermediate cell grouping level of anetwork), a location area update procedure is performed.

It is also possible to favor or discriminate against the reselection ofcertain cells via the intermediary of a CELL-RESELECT_OFFSET parameter,which is also broadcast by the BCCH channel of each cell.

This parameter may be positive or negative according to the value takenby the PENALTY_TIME parameter mentioned earlier.

The procedures disclosed above thus enable a mobile to communicate witha given network under the best possible conditions. A disclosure willnow be made below of the specific arrangements of the method and of thedevice according to the invention enabling the objects of the inventionas stated in the introduction to the present application to beeffectively fulfilled.

According to a first variant embodiment of the invention, it is possibleto prohibit, over a given geographical area, the routing of all thecalls from a given network to mobiles normally communicating with thisnetwork.

Such a prohibition may further be temporary, the prohibition being ableto be lifted or established at any desired moment.

FIG. 2 is a view similar to FIG. 1, which also depicts a schematic topview of three cells Z1, Z2, Z3 with which are associated threerespective relays R1, R2, R3. There are intercellular overlap areas inthis figure that enable the achievement of continuous coverage of aterritory by the network relays.

FIG. 3 a reproduces the three cells Z1, Z2, Z3 of FIG. 2. This figurealso depicts in parallel an area N, here situated at the center of thecells Z1, Z2 and Z3.

The area N covers an area that is usually covered by at least one of therelays R1, R2, R3.

It is pointed out that all the cells and areas in FIGS. 1 to 3 a aredepicted with a view to schematically representing in the form ofregular circular disks the shape and size of each of these areas, whichmay in reality be adapted according to the local topography, and thepropagation characteristics within each cell.

The area N contains a place within which control of communications iswanted; this place may be, for example, a theater, a church, etc., asmentioned in the introduction to the present application.

At the center of the area N that one wishes to protect in this way (as awhole, or partially, according to the relative transmission powers ofthe different relays used) a device D is placed for transmitting abeacon channel which is specific to it on one of the frequency channelsof the network considered.

This transmission has all the characteristics of a transmission on aBCCH channel via the relay of one of the network cells, i.e. it includesall the logical channels of such a transmission, and the parametersusually broadcast on a BCCH channel.

Furthermore, according to an important aspect of the invention, themobile network operator parameters the relays of each cell of the mobilenetwork situated close to the device D, so as to integrate into theBA(BCCH) list of each of these cells the “dummy BCCH” associated withthe transmission of the device D.

And in this way, the transmission channel of the device D is stored bythe neighboring cells of the device D, as an additional cell BCCH.

However, the device D is not connected to the network in any form ofembodiment of the invention; it operates completely autonomously.

The area N is thus treated as an additional cell. In addition, thenetwork operator controls all the parameters which are broadcast on thebeacon channel of the area N, which constitutes a “dummy BCCH”.

It will be noted that such a device can only be implemented by thenetwork operator, since the device uses one of the frequencies that areplaced at its disposal under a mobile operator license; in addition theparametering of this device requires knowledge of the characteristics ofthis particular network.

The power transmitted by the device D will determine the radius ofaction of this device, and may therefore be adjusted according to need.

Thus, the device D transmits like a relay of a cell on a time framing ofeight time intervals, only the first time interval being actually usedfor the transmission of the logical channels of this “dummy BCCH”.

D will thus transmit a BA(BCCH) list of BCCHs of the neighboring cellson this channel, this list having been parametered by the operator likeall the other data transmitted by the device D.

And a mobile located close to the device D and seeking to be connectedto the network will think it recognizes an additional network cell, allthe parameters broadcast by D being consistent with the characteristicsof the other cells, in particular neighboring ones.

The parameter of LAC (Location Area Code) must thus be identical to thatof the surrounding cells, to prevent any updating of location whenmobiles in idle mode enter the area covered by the device D.

The area N thus acts as a “phantom cell”, which can be chosen by themobiles located nearby during selection/reselection procedures. However,the device D, which is not in any way connected to the rest of thenetwork, in this first variant embodiment of the invention is only anillusion that is limited to transmitting.

And this “cell” N, when it is selected by a mobile at the end of aselection or reselection, does not put through any call to the mobile sothat the incoming communications to this mobile cannot succeed since thephantom “cell” N is not connected to the network.

FIG. 3 b schematically illustrates the distribution of the field levelsassociated respectively with the cell Z1 (level C1), with the area N(level C1 _(N)), and with the cell Z2 (level C1 ₂), along a line L thatis depicted in FIG. 3 a and that crosses a part of the area N.

It is seen in this figure that there is a central area within which thefield level C1 _(N) associated with the transmission of the device D isgreater than the field levels C1 ₁ and C1 ₂ of the relays of theneighboring cells; within this central area, marked N0 in FIG. 3 b, thiswill therefore be the “phantom cell” associated with the transmitter D,which will be chosen by the mobiles during selection/reselectionprocedures.

And once this “phantom cell” is chosen by a mobile, the mobile will onlylisten to the data transmitted on the dummy BCCH of D, the seven timeintervals normally associated with communication with the network in thecase of a normal cell being inactive.

Thus, over the first time interval the mobile will receive informationsimilar to that of a BCCH and will thus “think” that it is connected tothe network, but in reality it will not be able to receive calls fromthe network.

It is understood therefore that a mobile that is switched off or in idlemode entering the area N0 will not be able to receive any call from thenetwork, as long as it is camped on the “cell” N.

And it is possible according to the invention to parameter the datatransmitted on the dummy BCCH of the “phantom cell” at will; inparticular, it is possible to modify the CELL_BAR_ACCESS parameter ofthis “cell” N so as to bar it at will.

In the event that the “cell” N is thus barred, for example as a resultof a manipulation of the operator on the device (by operating a switch,or by programming a specific instruction in a memory associated with thedevice), or simply by a customer having requested the operator toinstall the device D in the heart of the area N, the mobiles previouslycamping on this “cell” N will automatically reselect a new cell of theoperator, the condition RS3 mentioned earlier being met, and may againreceive incoming calls.

Furthermore, the dummy transmission BCCH of the device D must beregistered in the list of neighboring cells BA (BCCH) transmitted byeach of the real cells of the network located nearby, which enables theselection/reselection of the “cell” N by a mobile entering the area N0to be protected.

A mobile in idle mode entering the area covered by the device will thuscamp on the area N as soon as the parameter C1 _(N) is greater than thefield levels parameter of the neighboring cells, i.e. as soon as themobile is located within the area N0, which constitutes the actualcontrol area.

And when the same mobile camping on the area N leaves the area N0, thereselection procedure which is iterative will be applied again, so as toallocate the mobile a new network cell where it may again receiveincoming calls and communicate with the network without any specialrestriction.

In the case of a mobile entering the area N0 while it is incommunication, and if the operator uses BA(SACCH) lists different fromthe BA(BCCH) lists used for the selection/reselection procedures, it ispossible to enable the mobile to complete its communication beforemaking it camp on the area N.

For this, the choice will be made not to register the dummy BCCH of the“cell” N in the BA(SACCH) lists of the neighboring cells of this area,so as to prevent any attempt at handover to this “cell” N.

Now in the case of a mobile being switched on while it is alreadylocated in the area N0, the initial selection may lead to the mobiletemporarily camping on a different cell from the “cell” N (for examplein the event that the mobile has stored a BA(BCCH) list before beingswitched off).

However, in this case, the reselection procedure will quickly lead themobile to camp on this “cell” N, thanks chiefly to the broadcasting bythe neighboring cells of BA(BCCH) lists containing the dummy BCCH ofthis “cell” N.

We have seen that the invention thus enables the effective filtering ofcommunications to mobiles associated with a given network, within adesired area.

It will be further noted that an advantageous aspect of the invention isthat its use does not disrupt the general operation of the mobilenetwork.

Now when a user wishes to call via the intermediary of this networkwhile he is in the area N0, given that the mobile is camped on the“cell” N, it transmits an access request to this “cell” N on the RACHlogical channel (which is the logical channel for initiatingcommunications over the time interval number 0 of the dummy BCCH).

These access requests will be unsuccessful since the “cell” N does nothave a receiver for receiving and processing such an access request.

Once a predefined maximum number of access attempts has been reached,corresponding to the parameter MAX_RETRANS, a cell reselection isautomatically initiated, the condition RS5 being met.

Thus the mobile will camp on one of the neighboring cells of the “cell”N and it may again access the network via the intermediary of this newcell, which is registered in the BA(BCCH) list of the “cell” N.

Once the communication is concluded, the mobile will return to camp onthe “cell” N due to the iterations of the reselection procedure.

Thus the first variant of the invention disclosed above can be used toprohibit mobiles of a given network located in a place where one wishesto filter communications, from receiving incoming calls, but allowsthese same mobiles to make calls via the intermediary of the network.

In a second variant of the invention, which reproduces the arrangementsof the first variant disclosed above regarding incoming calls (so thatthe mobiles associated with a given network cannot receive calls fromthis network when they are located in an area that one wishes tocontrol), the mobiles of the network are further prohibited from makingcalls to their network when they are located in this area to becontrolled.

However, arrangements are provided, as will be explained below, toenable these mobiles to let through certain calls even when they arelocated in the controlled area. In particular this enables thefulfillment of certain regulatory obligations, requiring the permanentfree access of mobiles to emergency numbers.

In this variant of the invention, the device D disclosed above is not asimple transmitter, but also has a simplified receiver for decoding thecontents of random access messages transmitted by the mobiles on theRACH channel.

The receiver of the device D can thus identify messages of the CHANNELREQUEST type transmitted by a mobile seeking to be connected to thenetwork. This CHANNEL REQUEST message is transmitted by the network'smobiles on a RACH logical channel of the cell—real or “phantom”—on whichthe mobile is camped.

Thus, the access request to the network from a mobile camping on the“cell” N as a result of the selection/reselection procedures will beidentified by the device D.

And the CHANNEL REQUEST messages transmitted on the RACH logical channelcomprise two parts:

-   -   a first part including a call reason parameter describing the        nature of the communication that the mobile requires. This        parameter may thus take different known values of the mobile and        the network, each value corresponding to a call reason:        emergency call, call resumption, response to a paging message,        communication channel request, another type of channel request        (signaling), location update, etc.    -   a second part comprising a reference for identifying the mobile.        This part enables the network relay—or here the receiver of the        device D—which receives the CHANNEL REQUEST to identify and        recognize each mobile.

And the device D, thanks to the call types file copied into its memory,can determine the reason for the access request from a mobile that iscamped on the “cell” N and which is seeking to call the network via theintermediary of this “cell”.

If the value of the call reason parameter corresponds to an emergencycall, (CHANNEL REQUEST starting with “101”), the device D does not sendany response to the mobile, thus causing a reselection of another cellby the mobile since the condition RS5 is then met, so that the emergencycall will be routed to the network via this other cell.

If now the call reason parameter corresponds to a different reason, thetransmitter of the device D transmits on its beacon channel an IMMEDIATEASSIGNMENT REJECT message, which indicates that no resource isavailable.

In this case the mobile “thinks” that the cell with which it seeks tocommunicate is unavailable. The mobile then waits for a time delayperiod T3122, set by the operator and capable of being between 0 and 255seconds in the case of the GSM standard, before transmitting a newCHANNEL REQUEST message on the RACH logical channel of the “cell” N.

And if the mobile persists at the conclusion of this period T3122 andtransmits a new CHANNEL REQUEST to the “cell” N, the device D will againrecognize the reason for the request and will again transmit anIMMEDIATE ASSIGNMENT REJECT message to the mobile (the mobile beingrecognized by the transmitter of the device D thanks to the second partof the CHANNEL REQUEST message, which enables the transmitter of thedevice D to transmit to this particular mobile).

It is obviously possible to define other types of calls having to berouted by causing a reselection, each of the different values of thecall reason parameter stored by the device being able to be marked inthe memory of D as having to give rise to reselection for call routing,or not.

Thus, in this second variant of the invention the mobiles associatedwith a given network are prohibited from accessing this network when themobiles are in a given area, certain types of calls, however, being ableto be routed.

And it is also recalled that while the invention was disclosed abovemore particularly with reference to the GSM standard, its application tonetworks operating according to other versions of this standard, orother standards, for example the UMTS standard, is naturallyconceivable. Thus, the numeric values appearing in this disclosure arerelated to the current versions of the standards referred to, and do notunder any circumstance constitute a limitation of the invention.

1. A method of filtering calls between a mobile network provided withfrequency channels and mobile telephones registered with this mobilenetwork, when the mobile telephones are located in a control area (N0),the mobile network comprising a plurality of cells (Zi) associated withrespective relays (Ri) each transmitting data specific to theirassociated cell through a beacon channel among one of the frequencychannels of the mobile network, the method comprising the steps of:parametering in neighboring cells of the control area of a frequencychannel of the mobile network corresponding to a transmission channel ofa transmitter (D) associated with said control area; transmitting on atransmission channel of said transmitter (D) through a BCCH logicalchannel; accepting the transmission of said transmitter by the mobiletelephones located within said control area (N0) as a beacon channeltransmission of an additional cell of the mobile network, so that thetransmission area of said transmitter is a candidate for theselection/reselection procedures, and neutralizing the incoming calls tomobiles having selected/reselected the transmitter of said control area;and associating no receiver with said transmitter (D), so that when amobile telephone transmits an access request on the RACH logical channelof said transmission channel, a reselection of neighboring cells will beautomatically initiated, for want of any response, said transmitter (D)being associated with reception means suitable for decoding the contentsof random access messages transmitted by the mobile telephones locatedwithin the control area (N0), so as to prohibit outgoing calls from saidmobile telephones to the mobile network; wherein said transmitter isnever connected to the mobile network so as to operate completelyautonomously, the reception means associated with the transmitter (D)are capable of identifying the CHANNEL REQUEST type access requestmessages transmitted by a mobile telephone seeking to be connected tothe mobile network, the transmitter is also associated with a memoryincluding a call types file, and with means for determining the reasonfor the access request of a mobile telephone, and the transmitterreceiving a CHANNEL REQUEST type access request: does not send anyresponse to the mobile telephone, causing a reselection of a mobilenetwork cell by the mobile, in the event that the reason for the mobiletelephone's access request corresponds to a determined reason, transmitson its transmission channel an IMMEDIATE ASSIGNMENT REJECT type messageindicating that no request is acceptable at the moment, in the eventthat the reason for the mobile telephone's access request does notcorrespond to said determined reason, so that the outgoing call from themobile telephone will only be routed to the mobile network if the reasonfor the call corresponds to a determined reason.
 2. The method asclaimed in claim 1, wherein the transmission of said transmitter (D) isperformed according to a time framing of eight time intervals, only thefirst time interval of each frame actually being used for thetransmission of certain logical channels.
 3. The method as claimed inclaim 1, wherein the transmitter (D) transmits a list of beacon channelsof cells which are its neighbors.
 4. The method as claimed in claim 1,wherein the location area parameter transmitted on the transmitter's (D)transmission channel is identical to the location area parameter of thebeacon channels of the surrounding cells.
 5. The method as claimed inclaim 1, further comprising providing means for changing the state of aparameter transmitted on the transmission channel of said transmitter,in order to bar the area associated with the transmitter so that themobile telephones camping on said area associated with the transmitterautomatically reselect a new cell (Zi).
 6. The method as claimed inclaim 1, wherein the transmission channel of said transmitter (D) isregistered in a list of beacon channels of neighboring cells, for eachcell (Zi) of the mobile network located close to said transmitter. 7.The method as claimed in claim 6, wherein mobile network cell (Zi)relays (Ri) broadcast on the BCCH channel, in addition to a first listof beacon channels of candidate cells for selection/reselectionprocedures, a second list of beacon channels of candidate cells for thehandover procedure, and the transmission channel of said transmitter,stored in the list of candidate cells for selection/reselection of theneighboring cells, is not stored in the second list of these neighboringcells.